A significant problem faced by medical professionals is the need for effective devices for the delivery of drugs to infants and children, in particular inhalable drugs in the form of aerosols, powders, vapors, or mists. Typical examples of such drugs that are widely used are asthma drugs, which employ pressurized metered dose inhalers (MDI) that deliver a measured dose of an aerosolized liquid or powder to a mouthpiece. In some cases, holding chambers are used, that serve to trap larger particles and provide a reservoir for suspended drug aerosol if the chamber is used with an inhalation mask. Other devices such as nebulizers are also in common use, and other diseases besides asthma are treatable by inhaled drugs. Most adults can simply use a mouthpiece in a device that administers an inhalable drug, and can coordinate their breathing with the use of an MDI or the flow of an inhalable drug. Children however lack the coordination, understanding, or communication skills necessary to use conventional drug inhalation devices. Accordingly, the use of an inhalation mask is required for children.
Breathing masks for use with children have several special requirements. The masks must be sized appropriately for children's' faces, which is not necessarily a matter of merely shrinking an adult-sized mask. The size and shape of the mask are critical to providing a good seal at the edges of the mask, to prevent leakage of medication to the eyes, and also to prevent loss of dose that would otherwise go to the lungs. Additionally, maintaining eye contact with the child may be important with young children, so a suitable mask should not cover the eyes or obscure vision. Also, a known problem with infants or children in the administration of inhaled medicaments is that existing masks often cause agitation and distress in a child, and makes them cry. If this occurs, the child will usually become uncooperative, and the disruption and uneven breathing during crying will probably prevent effective delivery of the drug substance to the lungs.
An approach to the problem of agitation caused by a mask, as previously disclosed by the instant inventors in U.S. Pat. No. 6,470,882, is the use of “soother device” in the mask for small children. A soother device is defined as a something the child can suck on, which has a calming effect. As set forth in U.S. Pat. No. 6,470,882, soother devices can be a “pacifier,” that is a plastic nipple that infants suck on, a bottle with a nipple, or a natural mothers breast. This concept takes advantage of the fact that small children, up to about age 18 months, are obligate nasal breathers, and infants are easily capable sucking from the breast or bottle without interrupting normal breathing. As disclosed in U.S. Pat. No. 6,470,882, a soother device inserted into the mouth section of an inhalation mask, covering the mouth and nose of an infant, can comfort a small child.
Another problem with infants and children in the administration of inhaled medicaments is that masks for children have hitherto been essentially shrunken versions of masks used for the administration of oxygen or anesthesia in adults. These prior art masks are sub-optimal. They tend to not fit well, tend not to have a good seal, and often fit poorly at the extremes in size, so a plurality of sizes is necessary to ensure a good fit. Another significant consideration is that children's faces change rapidly in the first few years of life, so a mask that is effective at say, 12 months of age may not provide a good seal at 18 months of age. Furthermore, most currently available masks have the airway for delivery of medication flow aligned with the mouth, and this design is used on most prior art children's medication masks based on adult mask designs. As noted elsewhere herein, infants are nasal breathers, so this alignment assures substantial (and undesirable) dead space in the mask.
Minimization of dead space is a desirable feature in a medication mask. Dead space is not a substantial problem with oxygen therapy or inhaled anesthesia, because the active gas for oxygen therapy or anesthesia is the fraction of active gas as a volume or partial pressure percentage of the active gas in ordinary air. The active gas can be used in excess at minimal cost, and metering of an absolute quantity of active substance is generally not important.
By contrast, with inhaled therapies for respiratory diseases, such as asthma, cystic fibrosis, bronchitis, etc., or for inhaled drugs for other conditions that are intended for deliver to the lungs, the absolute dose of the active drug usually is important. A certain quantity of medication is placed into the device, and the medical objective is to have as much of the medication inhaled into the lungs as possible. If there is a large dead space, a substantial amount of the active drug may be suspended in the dead space after an initial inhalation. That quantity of drug will be largely expelled from the dead space on the exhalation cycle, because all masks require an exhalation valve to vent exhaled air. With a small dead space, there is less volume for drug to remain suspended within the mask, so a greater percentage of the total dose will be inhaled, and a smaller quantity of drug will be expelled from the device on the exhalation.
In the administration of inhaled drugs, essentially two types of devices are in common use, nebulizers, and metered dose inhalers (MDI's). Nebulizers have a reservoir containing a drug solution through which a stream of air is bubbled through or over (typically). The air stream generates a mist or vapor, of atomized droplets suspended in air, which is conveyed to the mouth of the patient through a tube and a mouthpiece. In the case of invalid adults or small children up to the age of about 5 years, a mask is used.
MDI's are used for a wide variety of inhaled drugs, for example β-agonists, steroids, and anticholinergic drugs, for use in asthma, bronchitis, COPD, and other respiratory ailments. MDI's typically comprise a canister with a metering device and exhaust nipple. The canister contains a solution or suspension of a drug under pressure. A plastic actuator holds the canister and has a mouthpiece. Depressing the canister in the actuator actuates the delivery of a dose. Adults and older children can use the mouthpiece on the actuator directly, by coordinating their breathing with actuation.
In many cases, MDI's are used with a holding chamber or spacer, which is typically a tube about 10 cm long and 5 cm in diameter, that has a receptacle at the rear for holding an MDI, and a mouthpiece at the front end. The drug is introduced into the chamber, and then inhaled by the patient from the mouthpiece. Compared to an MDI without a chamber, the chamber is usually used to trap large particles that would otherwise lodge in the mouth or throat, causing irritation, rather than enter the lungs, which is the intended target organ. Additionally, the use of a spacer reduces or eliminates the need for the patient to coordinate their breathing with the actuation, since the drug can remain suspended in the chamber for several seconds until the patient inhales it.
MDI chambers can also be coupled to a breathing mask for use by patients who cannot use a mouthpiece, such as small children or incompetent patients. A caregiver actuates the MDI and the suspended drug substance enters the chamber and is then inhaled by the patient with no need to coordinate breathing or use of a mouthpiece. A suitable mask typically will have an inhalation valve and an exhalation valve. The inhalation valve is one-way, only allowing air to travel from the chamber into the mask, so that air with suspended drug is only drawn through the chamber during inhalation. The inhalation valve blocks exhaled air from entering the chamber and blowing drug out the back end vents. The exhalation valve is a one-way valve that allows exhaled air to vent out of the interior of the mask, but does not allow outside air to enter during inhalation. An example of a chamber and mask for use with an MDI is disclosed in U.S. Pat. No. 6,904,908.
As noted above, the fit of a mask is critical for maintaining a good seal. But, there is little empirical or scientific evidence for the design of pediatric masks for use in children. The issue of adequate fit is a particular problem in infants and young children whose face undergoes rapid and marked developmental change in the first few years of life. The lack of scientific evidence to support existing face mask design in this age group explains why infant/toddler face-mask design is suboptimal, particularly with regard to aerosol delivery where a tight seal is important in order to prevent leakage of drugs such as aerosolized corticosteroids, towards the eyes. A tightly fitting mask is also necessary to minimizing potentially sensitizing agents, such as antibiotics, from leaking into the caregivers' environment.